A diode such as a Schottky barrier diode (hereinafter, occasionally referred to as SBD), which is an example of a semiconductor device, is a semiconductor device that uses a rectifying action of a Schottky barrier which is a Schottky junction between a semiconductor layer and a metal layer. An SBD has characteristics such that the SBD can operate at higher speed than general PN junction diodes, and a forward voltage drop is small.
For example, in a switching power supply having such an SBD, when an emergency stop is performed in an emergency, a reverse voltage applied from the N type semiconductor layer toward the metal layer exceeds an upper limit of the breakdown voltage of the SBD (reverse breakdown voltage characteristics) in some cases. In a case where the reverse voltage exceeds the upper limit of the breakdown voltage, there is a concern that the characteristics of the SBD might be deteriorated.
FIG. 7 is a cross-sectional view showing an example of a conventional Schottky barrier diode. A Schottky barrier diode 1 shown in FIG. 7 includes a semiconductor substrate 2 that is, for example, an N type semiconductor. The semiconductor substrate 2 includes, for example, SiC (silicon carbide). In a part of the semiconductor substrate 2 on a one main surface 2a side, a guard ring 6 made of P type semiconductor is formed with a predetermined depth set in a thickness direction of the semiconductor substrate 2. Then, a metal layer 3 is formed on the one main surface 2a side of the semiconductor substrate 2, so as to be electrically-connected to a part of the guard ring 6. Additionally, a part of a bottom surface 3a of the metal layer 3 is in contact with the guard ring 6, and the other part thereof is in contact with the one main surface 2a, thus forming a Schottky junction with the semiconductor substrate 2.
The guard ring 6 includes a P+ type semiconductor portion 6a and a P− type semiconductor portion 6b which have different impurity concentrations from each other. The P− type semiconductor portion 6b is formed so as to cover side surfaces and a bottom surface of the P+ type semiconductor portion 6a. Additionally, a part of an exposed portion of the P+ type semiconductor portion 6a on the one main surface 2a of the semiconductor substrate 2, and a part of an exposed portion of the P− type semiconductor portion 6b on the one main surface 2a of the semiconductor substrate 2, are respectively in contact with parts of the bottom surface 3a of the metal layer 3.
This can improve the reverse breakdown voltage characteristics of the junction portion between the metal layer 3 and the semiconductor substrate 2.
Here, as a configuration different from that of the diode shown in FIG. 7, there is, for example, a Schottky barrier diode shown in Non-Patent Document 1. This Non-Patent Document 1 contains a description regarding the improvement of the reverse surge withstand capability.